KVM system for controlling computers and method thereof

ABSTRACT

A system for connecting a console device to computers comprising a graphic user interface menu apparatus for controlling the computers. The system comprises a user-side circuit, a central crosspoint switch, a plurality of computer-side circuits, a menu generating unit and a first switching device. The user-side circuit coupled to the console device receives electronic signals produced by the keyboard and cursor control device and creates a data packet. The central crosspoint switch is coupled to the user-side circuits, receives the data packets and routes the data packets. The computer-side circuits coupled to the central crosspoint switch and the computers receive the data packets from the central crosspoint switch for supplying the data packets to the computers. The menu generating unit generates a menu to be displayed. The first switching device alternately outputs a video signal of the menu data and a video signal from the computers to the video monitor according to a vertical synchronization signal.

FIELD OF THE INVENTION

The present invention generally relates to a KVM system for controllingcomputers and the method used for the same, and more particularly to asystem and method capable of controlling computers by processingkeyboard-video-mouse (KVM) signals.

BACKGROUND OF THE INVENTION

With rapid development of network engineering nowadays, akeyboard-video-mouse (KVM) switch interconnecting between a console anda plurality of computers is widely utilized to transmit KVM signalstherebetween for remotely controlling the plurality of computers fromthe console. An on-screen display (OSD) menu interface concept is raisedfor convenience of operation on controlling the plurality of remotecomputers. The user can directly select any one of the plurality ofcomputers from the OSD menu graphically presented on a displayer coupledto the console. Originally, it is designed only for connecting to fewercomputers due to a restricted remote control ability of the KVM switch.However, the design of the KVM switch has greatly been improved onaspects of functions. Especially, the number of computers joined to thenetwork can be greatly increased for complying with explosive growth ofvarious network neighborhoods. Even multiple KVM switches can beconstituted in daisy chain or cascade with each other. Sometime, thenumber of computers joined to the multiple KVM switches in daisy chainand cascade can reach up thousands. Obviously, as shown in FIG. 2, atraditional OSD menu is entirely composed of pure texts. It will belaboriously for any user to seek one by one and then access each desiredcomputer coupled to the KVM switch. For example, by multiple-levelcascades, e.g. five levels, or even eight levels, the user has tosequentially access these levels to find out the desired computer.Without a prepared detail list relative to all the computers, it will behardly found out the desired computer because the OSD menu composed ofpure text reveals little information related to the desired computer.Furthermore, the user has to waste lots of time to manipulate such anun-humanized interface to get better skill in operation.

Several prior arts adoptive of said traditional OSD menu technology havebeen disclosed in U.S. Pat. Nos. 5,721,842, 5,884,096, 5,937,176,6,112,264, 6,345,323, and U.S. Patent Application Publication No.20020087753. Further referring to FIG. 1, an exemplar showed that anon-screen display (OSD) menu was constructed by video signals generatedfrom an on-screen display (OSD) circuit 14, e.g. an OSD Chip. Then thevideo signals of the on-screen display (OSD) menu are transmitted to anoverlay circuit 12. The overlay circuit 12 is able to simultaneouslyreceive and combine the real-time video signals from a remote computerand the video signals of the OSD menu. While the user wakes the OSD menuup to select one of the computers from a monitor of the console device,an overlay signal generated by combining the real-time video signalsfrom the selected computer with the video signals related to the OSDmenu is outputted to the monitor. As a result shown in FIG. 2, atraditional OSD menu image graphed over a managing image from theselected computer is displayed on the central position of the monitor212. The OSD circuit 12 is used for generating the video signal of theOSD menu. An overlay circuit 14 is used to combine the real-time videosignal from the computer and the video signal of the OSD menu.Nevertheless, the signal processes for both the OSD circuit 14 andoverlay circuit 12 are greatly complicated. That is because that theoverlay circuit 12 according to a keyboard/mouse signal (OSD menu enablesignal) through the KVM switch 18 to determine whether the video signalof the OSD menu or the video signal from the computer is outputted forevery single pixel on the monitor. The signal processes of both the OSDand overlay circuit 12, 14 need a large number

Consequentially, there's a need to set forth a system and method forcontrolling remote computers having greater convenient operation andbetter-humanized interface.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a KVM system forcontrolling computers and the method for the same, which is able toactively generate a menu or an image constructed by real-time videosignals from at least one of the computers on a video monitor of aconsole.

Another object of the present invention is to provide a KVM system forcontrolling computers and the method for the same, which is able topreview a preview image constructed by video signals from the computersby picking up the menu image.

To accomplish the above objects, the present invention provides a KVMsystem for connecting a console device having a keyboard, cursor controldevice and video monitor to a number of computers. The KVM systemcomprises a user-side circuit, a central crosspoint switch, a pluralityof computer-side circuits and a graphic user interface menu apparatuscomprising at least a menu generating unit and a first switching device.The user-side circuit couples to the console device for receivingelectronic signals produced by the keyboard and cursor control deviceand for creating a data packet that includes the electronic signals. Thecentral crosspoint switch couples to the user-side circuits and includesa number of inputs and a number of outputs, the central crosspointswitch receives the data packets from one of the inputs and routes thedata packets to one or more of the outputs. The plurality ofcomputer-side circuits couple to the central crosspoint switch and thecomputers and receives the data packets transmitted from the centralcrosspoint switch for supplying the data packets to one of thecomputers. The menu generating unit of the graphic user interface menuapparatus generates a menu data. The first switching device outputs themenu data or a real-time video signal from one of the computers to thevideo monitor.

Furthermore, the graphic user interface menu apparatus comprises animage capture device deposed between the console device and thecomputers to capture the video signals from the computers to constructthe preview images. The graphic user interface menu apparatus furthercomprises a processor, a memory and a video signal generator. Theprocessor controls all devices in the graphic user interface menuapparatus. The memory is used to pre-store the preview imagestemporarily. The video signal generator coupled to the first switchdevice, generates the menu data to the video monitor.

A method for controlling a number of computers principally comprises thesteps of:

generating menu data by a menu generating unit; and

selectably outputting the menu data or real-time video signals from oneof the computers via a first switching device to a video monitor by afirst switching device, thereby displaying a menu or an imageconstructed by the real-time video signals on the video monitor.

Beside, the present invention further comprises the following steps of:

capturing a video signal from the computers to construct preview imagedata on the video monitor by an image capture device;

pre-storing the preview image data in a memory;

displaying a preview image on the video monitor according to the previewimage data by manipulating the menu.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system with a traditional OSD menu on the videomonitor according to the prior art;

FIG. 2 illustrates a frame with traditional OSD menu composed of textson the video monitor, according to the system of FIG. 1;

FIG. 3 illustrates a KVM system having a graphic user interface menuapparatus located in a central crosspoint switch of the KVM systemconnected between a console device including a keyboard, cursor controldevice and video monitor and a number of computers, according to a firstembodiment of the present invention;

FIG. 4 illustrates a KVM system having a graphic user interface menuapparatus located in a user-side circuit of the KVM system connectedbetween a console device and a number of computers, according to asecond embodiment of the present invention;

FIG. 5 illustrates a KVM system having a graphic user interface menuapparatus located in a central crosspoint switch of the KVM system thatthe KVM signals transmitted between a console device and a number ofcomputers according to a third embodiment of the present invention;

FIG. 6 illustrates a KVM system having a graphic user interface menuapparatus further comprising a synchronization signal source for themenu generating unit according to a fourth embodiment of the presentinvention;

FIG. 7 illustrates a result of alternately switching two framesconstructed by the real-time image of the computer and the image of theOSD menu according to an embodiment of the present invention;

FIG. 8 illustrates a frame, which shows a graphic user interface menuinitially activated after a keystroke command of the keyboard;

FIG. 9 illustrates a frame that shows a graphic user interface menuimage arranged side by side with four preview images relative to fourdifferent computers;

FIG. 10 illustrates a frame that shows a graphic user interface menuimage arranged side by side with a specific preview image from a singleselected computer; and

FIG. 11 illustrates a frame that a viewing screen relative to either theconsole device or the selected computer is being switched by ascrolling-down submenu in the graphic user interface menu.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIG. 3, which illustrates a KVM system according to afirst embodiment of the present invention, principally including auser-side circuit 202, a central crosspoint switch 204 and a pluralityof computer-side circuits 206. The central crosspoint switch 204, suchas a KVM switch, having a number of inputs and a number of outputs, isconnected to a console device including a keyboard 216, a cursor controldevice 214 which can control the movement of the cursor, such as amouse, a touch pad or a track ball, and a video monitor 212 through theuser-side circuit 202, and alternatively is connected to a plurality ofcomputers 218 (i.e. PC#1˜32) through the computer-side circuits 206. Inapplication, the central crosspoint switch 204 receives the data packets(or a differential signal, or analog signal, depending on acommunication specification adaptive of the KVM switch 204) from one ofthe inputs and routes the data packets to one or more of the outputsthereof. The plurality of computer-side circuits 206 receives the datapackets transmitted from the central crosspoint switch 204 for supplyingthe data packets to at least one of the computers 218. Furthermore, theKVM system employs a graphic user interface menu apparatus located insaid central crosspoint switch 204. For extending a communicationdistance between the console device and the number of computers 218, theuser-side circuit 202 and the computer-side circuit 206 are respectivelyadopted, additionally. The graphic user interface menu apparatusprincipally includes a menu generating unit 104, a first switchingdevice 110, a image capture device 102, a processor 106, a video signalgenerator 108, a memory 112 and a second switching device 114.Specifically, the menu generating unit 104 can be realized by an ASIC togenerate the graphic user interface menu or even just a storing devicethat stores a special software program for generating the graphic userinterface menu to be displayed on the video monitor 212.

In contrary to the typical skill, a signal-controlling process of theKVM system according to the present invention is described below. First,the user-side circuit 202 coupled to the console device is used toreceive electronic signals produced by the keyboard 216 and cursorcontrol device 214, and create a data packet that contains theelectronic signals. Part of inputs of the central crosspoint switch 204are used for receiving the data packets from one of the console devices,and part of outputs of the central crosspoint switch 204 are used forrouting the data packets from the user-side circuit 202 to one or moreof the outputs. By the computer-side circuits 206, the computer 218receives the data packets transmitted from the central crosspoint switch204.

The menu generating unit 104 of the graphic user interface menuapparatus pre-stores menu data in the apparatus for generating aspecific graphic user interface (GUI) menu image on the video monitor212. The image capture device 102 of the graphic user interface menuapparatus is operative to capture video signals from the computer 218 toconstruct image files convenient to the user's preview, which arerespectively pre-stored in a memory 112, temporarily. The processor 106controls all units in the graphic user interface menu apparatus. Thevideo signal generator 108 parses the menu data pre-stored in the menugenerating unit 104 to generate the video signals that can construct aGUI menu image on the video monitor 212. The first switch device 110realized as a multiplexer, according to the user's command, selectablyoutputs the menu data or the real-time video signal from the selectedcomputer to the video monitor of the console device, as switchingdifferent viewing screen outputs. That is, once the image of the menudata is presented on the video monitor of the console, the real-timevideo signal from the selected computer is blocked by the first switchdevice 110. Therefore, the real-time video signal cannot be output tothe video monitor of the console device. As a result, a menu without anybackground is presented on the video monitor of the console device.

In the first preferred embodiment, the graphic user interface menuapparatus further includes a second switching device 114, which islocated in central crosspoint switch 204 for selectably outputting thereal-time video signals from the computer 218 or other computers to thefirst switching device 110. The second switching device 114 can be amultiplexer or a demultiplexer.

The communication line 302 is for transmitting video signals and thecommunication line 304 is for transmitting keyboard, cursor controldevice signals. Furthermore, for a differential data type, the graphicuser interface menu apparatus further includes an analog-to-digitalconverter 116, a differential-to-analog converter 118 and ananalog-to-differential converter 120. The differential-to-analogconverter 118 transforms the differential video signals into analogvideo signals. The analog-to-digital converter 116 transforms the videosignals into video data, which is consumed by the image capture device102 to construct the preview image. The analog-to-differential converter120 coupled to the video signal generator 108 transforms the analogvideo signals into the differential video signals used for the firstswitching device 110.

Besides, the transceiver, UART and GPIO shown in figures are mostlyrelated with processing keyboard, cursor control device signals.

Please refer to FIG. 4. It illustrates a KVM system having a graphicuser interface menu apparatus located in a user-side circuit, accordingto a second embodiment of the present invention. In this secondembodiment, the graphic user interface apparatus merely receives thevideo signals from the central crosspoint switch 204 without need ofselecting the computer 218. Meanwhile, the video signals (i.e. RGBsignals for the video monitor 212 shown in FIG. 4) are generated by thevideo signal generator 108 and are then transmitted through the firstswitching device 110 to the video monitor 212 of the console device foruser's view.

As aforementioned, the transceiver, UART and GPIO additional keyboard,cursor control device controller (KB/MS controller) shown in figures aremostly related with processing keyboard, cursor control device signals.

Please refer to FIG. 5. It illustrates a KVM system having a graphicuser interface menu apparatus located in a central crosspoint switch204, according to the third embodiment of the present invention. The KVMsignal is transmitted through the system in the form of analog.Therefore, in this third embodiment with usage of analog keyboard,video, cursor control device data, an analog-to-digital converter isemployed to transform the analog video signals into data packets forprocessor 106 and other related component.

Please refer to FIG. 6. It illustrates a system having a graphic userinterface menu apparatus according to a fourth embodiment of the presentinvention, which includes a synchronization signal source for the menugenerating unit 122. The menu generating unit 104 mentioned in FIG. 3can be implemented in a form of software. However, the menu generatingunit 122 shown in FIG. 6 with a synchronization signal source 124 isimplemented in a form of hardware. The present invention provides thesynchronization signal source 124 for the menu generating unit 122 togenerate an OSD menu. For example, the IC production named “MTV021”manufactured by Myson Technology. However, the OSD menu only shows upalone in the video monitor 212 of the console device as same as theprevious three embodiments. That is, there is no image from the computerexisting in the background of the OSD menu. The first switching device110 outputs either the menu data or the real-time video signals from oneof the computers to the video monitor. The menu generating unit 122generates a graphic user interface menu like the first to thirdembodiment.

Please refer to FIG. 7. Alternatively, to avoid monotone and supply moreinformation, when the user watches the monitor, the present inventionstill can display the real-time video signals of the computer for theuser. Please refer to FIG. 6 with FIG. 7. It shows that a verticalsynchronization signal (VSYNC) 124-1 is provided to the first switchingdevice 110 to control the outputting of the first switching device 110.The vertical synchronization signal 124-1 can come from the same sourceas synchronization signal 124 (VSYNC) or a different source from thesynchronization signal 124. Originally, the synchronization signal's 124source is from the computer 218 or other computer. The purpose of thesynchronization signal (horizontal and vertical synchronization signal)is to synchronize the video signals (red, green, blue colors) of the OSDmenu when outputted to the monitor. Here, the vertical synchronizationsignal 124-1 is employed as a toggle signal to control the outputting ofthe first switching device 110. Generally, both the verticalsynchronization signal 124 and 124-1 are from the same source of thecomputer.

Meanwhile, the added vertical synchronization signal 124-1 is employedto determine whether the real-time video signals from the computer orthe video signals of the OSD menu will be outputted to the monitor.Therefore, the GUI apparatus can use vertical synchronization signal124-1 to control the first switching unit 110 alternately outputting themenu data and the real-time video signals from the computer to the videomonitor 212. The first switching unit 110 outputs the video signals ofthe order: frame 1-frame 2-frame 3-frame 4 alternately as shown in FIG.7. The odd frames, such as Frames 1 and 3 images, are constructed by thevideo signals from the computer, the even frames, such as Frames 2 and 4images, are constructed by the video signals from the OSD menugenerating unit. For example, at first, the first switching device 110outputs the Frame 1. Thereafter, once the first switching device 110receives the vertical synchronization signal 124-1, the first switchingdevice 110 alters to output the Frame 2 constructed by the video signalsfrom the OSD menu generating unit. After that, once the first switchingdevice 110 receives the vertical synchronization signal 124-1 again, thefirst switching device 110 alters to output the Frame 3 constructed bythe video signals from the computer. By high speed switching between theabove two video signals alternately, resulting in video monitor 212presents the real-time image of the computer and the image of the OSDmenu just like an animation consisting of repeating films (as the visualeffect shown in the right part of FIG. 7.). Generally speaking,according to the VESA standard, the frequency of the verticalsynchronization signal 124-1 can be 60 Hz, 75 Hz or even higher.

When the user uses a keystroke or a sequence of keystrokes of thekeyboard to activate a GUI menu, the menu generating unit 122 accordingto the keystroke generates a menu data. Then a graphic user interfacemenu constructed by the menu data is shown on the video monitor, aspresented in FIG. 7. In the device management explorer area 502, aplurality of icons representing the devices are shown in a tree schema.The user can easily understand the real connection of all devices fullyat a glance, even through a real connection in cascade, e.g. fivelevels, or even eight levels. Unlike the prior art, a text-only OSD menurevealing little information may easily confuse the user. In the stageof the preview area 504, a preview image from the selected computer willshow up on user's demand. In the embodiment, the preview area 504 isblank when the graphic user interface menu is activated initially.

Please refer to FIG. 8. The frame shows that a graphic user interfacemenu image arranged side by side with four preview images from four ofthe computers. After the graphic user interface menu is activated asshown in FIG. 7. The user can select the KVMs (central crosspointswitch'indicators) or the PC (computer's indicators) in the devicemanagement explorer area 502. For example, the user selects the KVM1,then each preview images of the PC1, PC2, PC3 and PC4 pops up in quarterof the preview area 504 correspondingly. The preview images 504-1,504-2, 504-3 and 504-4 are corresponding to the computers PC1, PC2, PC3and PC4. Specifically, the preview images of the computers are capturedby the image capture device and pre-stored in the memory in a form ofstatic picture. The timing of capturing video signals from the computersto construct preview images by an image capture device 102 can be settledown in a predetermined interval regularly, e.g. 1 second or 250 secondsor after the user has selected the specific KVM or PC in the graphicuser interface menu. The image capture device captures the previewimages from the video output port of the computers through thecommunication line 302, which is specifically for transmitting videosignals, e.g. VGA port.

Please refer to FIG. 9. To follow the FIG. 7 and FIG. 8, the frame thata graphic user interface menu image arranged side by side with specificthe preview image of the selected computer with the menu image. Forinstance, the user also can explore the tree schema shown in the devicemanagement explorer area 502 and select the desired computer (PC1). Thepreview image 506 of the PC1 pops up as shown. Furthermore, please referto FIG. 10. The frame shows that the user is given more power to switchthe viewing screen at the console device or control the selectedcomputer, through a pull-down submenu in the graphic user interfacemenu. Following user's operation mentioned in FIG. 9, a pull-downsubmenu 508 shown in the preview image 506 providing more functionsdesigned in advance. For instance, the user can switch viewing screenfrom the menu image to the real-time video signals from the selectedcomputer by selecting the FUNCTION 1 in the pull-down submenu 508, i.e.controlling the outputting source of the first switching device 110.

Please refer to FIG. 3 and FIG. 9. In these cases, the user commands themenu generating unit 104 to generate a corresponding menu data by akeystroke or a sequence of keystrokes (by the cursor control device 214or the keyboard 216). Then the first switch device 110 outputs menu datato the video monitor 212 of the console for displaying the menu on thevideo monitor 212. When the user selects one of specific icons relativeto computers in the device management explorer area 502 of the menu, apreview image 506 corresponding to the computer is showed in the stageof the preview area 504. Therefore, the user can actively know thestatus of the selected device. Thus, the user can control the firstswitch device 110 to selectably output the menu data or the real-timevideo signals from the selected computer on demands.

In conclusion, the proposed invention is able to provide a system andmethod for controlling computers, which is able to actively output amenu or an image constructed by real-time video signal from at least oneof the computers on a video monitor of a console. The graphic userinterface apparatus captures the video signals from the computers toconstruct preview images of the computers to be employed in the graphicuser interface menu for user's preview.

As is understood by a person skilled in the art, the foregoing preferredembodiments of the present invention are illustrative rather thanlimiting of the present invention. It is intended that they covervarious modifications and similar arrangements be included within thespirit and scope of the appended claims, the scope of which should beaccorded the broadest interpretation so as to encompass all suchmodifications and similar structure.

1. A system for connecting a console device including a keyboard, cursorcontrol device and video monitor to a number of computers, the systemcomprising: an user-side circuit coupled to the console device forreceiving electronic signals produced by the keyboard and cursor controldevice and for creating a data packet that includes the electronicsignals; a central crosspoint switch, coupled to the user-side circuits,including a number of inputs and a number of outputs, the centralcrosspoint switch receiving the data packets from one of the inputs androuting the data packets to one or more of the outputs; a plurality ofcomputer-side circuits coupled to the central crosspoint switch and thecomputers, for receiving the data packets transmitted from the centralcrosspoint switch and for supplying the data packets to one of thecomputers; a menu generating unit for generating menu data; and a firstswitching device, selectably outputting the menu data or a real-timevideo signal from one of the computers to the video monitor.
 2. Thesystem according to claim 1, further comprises an image capture device,deposited between the console device and the number of computers,capturing a video signal from at least one of the computers to constructat least one preview image;
 3. The system according to claim 2, whereinthe image capture device is located in the user-side circuit.
 4. Thesystem according to claim 2, wherein the image capture device is locatedin the each of the computer-side circuits.
 5. The system according toclaim 2, wherein the image capture device is located in the centralcrosspoint switch.
 6. The system according to claim 1, furthercomprising a video signal generator, coupled to the first switch device,generating the video signal of outputting the menu data to the firstswitch device.
 7. The system according to claim 1, further comprising asecond switching device, for selecting one of the computers to outputthe real-time video signal from the one of the computer to the firstswitching device.
 8. The system according to claim 1, further comprisingan analog-to-digital converter to transform the video signal into avideo data.
 9. The system according to claim 8, further comprising adifferential-to-analog converter to transform the video signal into ananalog video signal.
 10. The system according to claim 9, furthercomprising an analog-to-differential converter, coupled to the videosignal generator for transforming the analog video signal into thedifferential video signal transmitted to the first switching device. 11.The system according to claim 1, wherein the menu generating unitgenerates an OSD menu.
 12. The system according to claim 11, furthercomprising a synchronization signal source for the menu generating unit.13. The system according to claim 11, further comprising a verticalsynchronization signal source for the first switching device.
 14. Thesystem according to claim 13, wherein the first switching unitalternately outputs the menu data and the real-time video signals fromone of the computers to the video monitor according to thesynchronization signal.
 15. A graphic user interface menu apparatusapplied in a connection between a console device including a keyboard,cursor control device and video monitor and a number of computers, theapparatus comprising: a menu generating unit for generating menu data;and a first switching device, selectably outputting the menu data or areal-time video signal from one of the computers to the video monitor.16. The apparatus according to claim 15, further comprising an imagecapture device, deposed between the console device and the computers,for capturing a video signal from at least one of the computers toconstruct at least one preview image.
 17. The apparatus according toclaim 15, further comprising a video signal generator, coupled to thefirst switching device, generating the video signal of outputting themenu data to the first switching device.
 18. The apparatus according toclaim 15, further comprising a second switching device, for selectingone of the computers to output the video signal from the one of thecomputer to the first switching device.
 19. The apparatus according toclaim 15, further comprising an analog-to-digital converter to transformthe video signal into a video data.
 20. The apparatus according to claim15, further comprising a differential-to-analog converter to transformthe video signal into an analog video signal.
 21. The apparatusaccording to claim 20, further comprising an analog-to-differentialconverter, coupled to the video signal generator for transforming theanalog video signal into the differential video signal transmitted tothe first switching device.
 22. The apparatus according to claim 15,wherein the menu generating unit generates an OSD menu.
 23. Theapparatus according to claim 14, further comprising a synchronizationsignal source for the menu generating unit to generate the menu data.24. The system according to claim 15, further comprising a verticalsynchronization signal source for the first switching device.
 25. Thesystem according to claim 24, wherein the first switching unitalternately outputs the menu data and the real-time video signals fromone of the computers to the video monitor according to the verticalsynchronization signal.
 26. A method for controlling a number ofcomputers in a connection from a console device including a keyboard,cursor control device and video monitor, wherein the method comprisingthe steps of: generating menu data by a menu generating unit; andoutputting the menu data or a real-time video signal from one of thecomputers to the video monitor according to a vertical synchronizationsignal.
 27. The method according to claim 26, further comprising a stepof capturing a video signal from at least one of the computers toconstruct at least one preview image by an image capture device beforethe step of generating the menu.
 28. The method according to claim 26,further comprising a step of generating the menu data to the firstswitching device by a video signal generator before the step ofoutputting the video signal.
 29. The method according to claim 26,further comprising a step of transforming the video signal into a videodata after the step of selecting one of the computers to output thevideo signal by an analog-to-digital converter.
 30. The method accordingto claim 29, further comprising a step of transforming the video signalinto an analog video signal before the step of transforming the videosignal into a video data by a differential-to-analog converter.
 31. Themethod according to claim 30, further comprising a step of transformingthe analog video signal into the differential video signal after thestep of generating the menu data by an analog-to-differential converter.32. The method according to claim 26, further comprising a step ofcapturing a video signal from at least one of the computers to constructat least one preview image, combining the preview image with the menuimage after the step of outputting the menu data.